Although it may have other uses, the fluid check valve of the invention is intended to provide leak protection in oil-cooled electric feeder cable piping systems. High-power electric feeder cables operating at, for example, 370 kv (kilovolts) become heated during use and it is therefore conventional to encase the cable in piping to create a path through the cable for slow circulation of dielectric oil to cool it. The oil is under high pressure, usually on the order of 200 psi (pounds per square inch). Such oil-filled electric power cable usually extends considerable distances overland, or buried in the ground to provide electric service to factories, homes and other places. If the cable becomes damaged with resulting rupture and leakage of the oil, not only will the cable begin to overheat but the seepage and loss of oil may create other well known difficulties. Moreover, replacement of lost oil involves considerable expense. It is therefore conventional to provide cooling oil stop joints at particular locations along the cable distance, such as at transfer points, so as to isolate the sequential lengths of the cooling system from each other. Thus, leakage occurring at any location along the feeder cable is localized for easier detection and repair, and for limiting the loss of oil.
However, usually all of the oil in any such isolated cable length is lost upon leakage occurring anywhere along that length. Thus, because these conventional stop joints are located at the cable transfer points the distances between them are relatively long. Accordingly, it is difficult to isolate and locate the point of the leakage, because all of the considerable length of cable between any two stop joints must be inspected.
Electrical cables, cooled by flow of oil under pressure, which employ conventional stop joints at spaced locations along the cable to divide the cable into sections that can be isolated from each other to prevent drainage of the entire cable in the case of a break or leakage in one cable section, and which have bypass pipes equipped with valves at the stop joints, are shown in Bennett U.S. Pat. Nos. 1,975,075 and 1,969,721, granted in 1934. The disclosures of these patents are incorporated herein by reference for their showing of stop joints and valved bypass pipes in conjunction with oil-cooled electrical cables.
It would obviously be advantageous if many more stop joints could be provided along the entire distance of the feeder transmission, so as to permit better pinpointing of any leakage location. However, such has not been possible using conventional one-way stop valves as stop joints, because flow continues through all the valves on the upstream side of the leak until pumping is discontinued.
The two-way check valve of this invention provides such advantage. That is, it is operable to close in either direction in response to rupture or significant leakage occurring in the fluid-carrying conduit on either its upstream side or its downstream side, and the valve will automatically reopen when normal pressure or flow conditions have been reestablished within the conduit. This fully automatic operation permits the valve to be located at remote or otherwise inconveniently accessible locations within the line, permitting comparatively short lengths of cable between such check points. Moreover, it can be installed in any valve orientation, whether vertical, horizontal, or at any angle to the horizontal, yet it will still operate dependably in the intended manner.